The present invention relates to electrical cartridge fuselinks for protecting electrical and electronic equipment and, more particularly, to cartridge fuselinks intended to rupture at low current values.
Cartridge fuselinks having low current ratings utilize fusible wires of extremely small diameter. In many instances, they are barely visible to the naked eye. Hence, they are difficult to handle and often comprise metals or alloys which are difficult to solder. To facilitate the manufacture of cartridge fuselinks having these small diameter fuse wires and improve their operational reliability, it is known to mount the fusible wire on an insulating support with its opposite ends electrically connected to conductive end portions of the support and then to assemble the fuse element thus formed with an insulating barrel or tube. The fuse element is disposed within the insulating barrel and its conductive end portions are electrically connected to metal end caps or terminals fastened to opposite ends of the barrel. A number of different constructions of this type are disclosed by the prior art, for example, U.S. Pat. Nos. 2,576,405 (C. L. M. McAlister), 3,348,007 and 3,568,122 (both issued to A. Urani), 3,530,505 (E. Salzer) and U.K. Pat. No. 768136 (Belling & Lee Ltd).
McAlister and the first of the Urani patents disclose fuse elements in which the insulating support is of approximately the same length as the insulating barrel and a short length of fusible wire is disposed diagonally across the support and is soldered between conductive layers on the support which extend from its opposite ends to adjacent the centre of the support. The fusible wire is prevented from contacting the support by an aperture or rebate therein. When the fuse element is assembled within an insulating barrel the conductive layers are soldered to the end caps. The second Urani patent describes an arrangement in which the insulating support is somewhat shorter than the insulating barrel and the conductive layers at opposite ends of the support are connected to the adjacent end caps on the barrel by lead wires soldered to the conductive layers and the end caps. Salzer discloses a more complicated construction in which the insulating support serially mounts a plurality of fusible wire sections interconnected by conductive ribbon sections on the support and connected to the end caps of the cartridge fuse by such ribbon sections. The fusible wire sections are welded to the conductive ribbons and the outer ribbons are soldered to the end caps. The Belling & Lee patent describes a fuse element in which a fusible wire is disposed along the length of an elongated insulating support of approximately the same length as the insulating barrel and is clamped to opposite ends of the support by means of metal clips which have longitudinally projecting tongues. An aperture in the centre of the support prevents the fusible section of the wire from contacting the support. The fuse element is positioned in an insulating barrel and the tongues at opposite ends of the support project through apertures in end caps attached to the barrel and are bent over and secured to the outside of the associated end caps by soldering or spot welding.
Other patents of generally background interest are U.S. Pat. No. 1,921,392 (F. C. La Mar) and German Pat. Nos. 368033 (W. Pudenz) and 426301 (N. Sandor).
The prior art constructions described above are all relatively expensive to manufacture and do not lend themselves to the mass production of cartridge fuselinks. It is an object of the present invention to provide a method of manufacturing cartridge fuselinks of the kind described which facilitates the use of mass production techniques and enables the production of a relatively inexpensive fuselink of novel construction.